Daily and seasonal variations detected in salivary biomarkers in horses in a recent study should be taken into account when interpreting saliva test results, according to researchers.
Researchers in Spain and Portugal noted increasing interest in the use of salivary biomarkers in the veterinary field, since saliva is usually easy to obtain and its collection causes less stress than blood sampling.
“However, our knowledge of the possible factors related to daily and seasonal variations in salivary biomarkers is still in its infancy,” María Contreras-Aguilar and her colleagues wrote in the open-access journal Animals.
Scientists from the University of Murcia in Spain and the University of Évora in Portugal designed an experiment to learn more about daily and seasonal variations in several salivary biomarkers in horses.
Their preliminary study used five healthy mares, from whom saliva samples were taken from 6.30am to 8.30pm every two hours over two consecutive days in winter and spring.
They tested for levels of integrated cortisol, salivary alpha-amylase, lipase, total esterase, butyrylcholinesterase, adenosine deaminase, γ-glutamyl transferase, creatine kinase, urea, total bilirubin, total protein, and phosphorus.
Changes throughout the course of the day were observed for cortisol, salivary alpha-amylase, total esterase, butyrylcholinesterase, adenosine deaminase and creatine kinase. All except salivary alpha-amylase showed a clear daily rhythm.
They also found that the values obtained for salivary alpha-amylase, lipase, and butyrylcholinesterase were significantly different between seasons, with different daily rhythms for cortisol, total esterase, butyrylcholinesterase and adenosine deaminase, depending on the season.
“In conclusion, this pilot study indicates that the time of the day and the season influence salivary analytes in horses.
“Therefore, these factors should be considered for the interpretation of these analytes when measured in horse saliva.”
Discussing their findings, the researchers said the significant differences in total esterase and butyrylcholinesterase seen between two consecutive days of sampling suggest that different external factors can easily influence these parameters.
“Notably, in the cases of cortisol, total esterase and butyrylcholinesterase, the increases that occurred at certain times of the day reached the range of the values that were found in situations of acute stress or diseases.
“This reinforces the need for saliva samples to be obtained during the same period of the day and/or season for comparative purposes.”
The study team acknowledged that the number of horses used in the study was relatively low. “Therefore, this study should be considered a pilot project, and the results should be confirmed in a larger population.
“In addition, the possible variations in these rhythms, depending on the breed and conditions such as fitness and body condition score, should also be evaluated.”
The study team comprised Contreras-Aguilar, Damián Escribano, Jose Cerón, Fernando Tecles, Alberto Quiles and María Hevia, all with the University of Murcia; and Elsa Lamy, with the University of Évora.
Contreras-Aguilar, M.D.; Lamy, E.; Escribano, D.; Cerón, J.J.; Tecles, F.; Quiles, A.J.; Hevia, M.L. Changes in Salivary Analytes of Horses Due to Circadian Rhythm and Season: A Pilot Study. Animals 2020, 10, 1486.